Selective mirror-image reversal of ciliary patterns inTetrahymena thermophila homozygous for ajanus mutation

Abstract

The development of the oral apparatus (OA) and of neighboring ciliary structures ofTetrahymena thermophila was analyzed in cells homozygous for ajanus (jan A) mutation plus a recessiveenhancer of janA (eja). Such cells frequently possess two OAs located on opposite sides of the cell, a primary (1°) OA previously reported to be normal, and a secondary (2°) OA previously reported to express a mirror-reversal of right-left asymmetry. This study confirms the reality of a reversal in the gross orientation of membranelles in most developing 2° OAs. It also shows that there is a reversal of asymmetry in the pattern of resorption of basal bodies of ciliary rows adjacent to the 2° OA, and in the arrangement of basal-body couplets making up the portion of the apical "crown" of the cell situated close to the 2° OA. However, the locations at which membranelles of the 2° OA become modified during late phases of oral development remain normal, so that membranelles of 2° OAs are superimposable on those of 1° OAs. In addition, the membranelles of 2° OAs frequently undergo a rotation during the final phases of oral development, so that even their spatial orientation becomes normal. This mixture of reversed and normal features can be accounted for by postulating a superimposition of a reversed largescale asymmetry on a normal local asymmetry of ciliary units. This postulate predicts that no single mutation can bring about a complete mirror-image reversal of ciliary patterns.1° OAs appear normal by light microscopy. However, detailed analysis of SEM, preparations of isolated 1° OAs indicate subtle abnormalities of basal body arrangement in some of these OAs.

Keywords: Cell surface patterns; Cellular asymmetry reversal; Ciliate development; Mutations affecting patterns; Tetrahymena thermophila.